Method for manufacturing a multilayer semiconductor structure that includes an irregular layer

ABSTRACT

A method for manufacturing a multilayer semiconductor structure that includes an irregular layer. In an embodiment, the method includes providing a layer of irregular material on a donor substrate. The irregular layer has a flat face at an interface with the donor substrate, and has an opposite, irregular face. Next; a weakened zone is created at a predetermined depth within the donor substrate. An intermediate layer of material is then provided that covers the irregular face of the irregular layer, the intermediate layer providing a substantially flat surface. The substantially flat surface of the intermediate layer is then bonded to a receiver substrate, and the donor substrate is detached along the weakened zone to form the multilayer semiconductor structure. The multilayer structure includes an useful layer, the irregular layer, the intermediate layer and the receiver substrate, wherein all of the irregular material of the irregular layer is present in the structure.

BACKGROUND ART

This invention generally relates to a method for manufacturing amultilayer semiconductor structure that includes a layer of irregularmaterial. In an embodiment, the method includes providing a layer ofirregular material on a donor substrate, creating a weakened zone in thedonor substrate, providing an intermediate layer that covers the surfaceof the irregular layer and provides a substantially flat surface,bonding the substantially flat surface of the intermediate layer to areceiver substrate, and detaching the donor substrate along the weakenedzone to form the multilayer semiconductor structure.

The words “donor” and “receiver” correspond to the “active layer” and tothe “support” of the wafer, respectively. These terms may also mean“top” and “base”, respectively, at times. In addition, the expression“layer of irregular material” means a layer having at least one surfacewhich is not regular (according to this definition, a layer ofsingle-crystal silicon is typically a regular layer).

A layer of irregular material is, within this text, understood to be alayer of which at least one free surface has a roughness and a flatnessgreater than a value of a few angstroms expressed in terms of root meansquare (RMS) values. Conversely, in this text, a layer is regular if theroughness of its free surfaces is less than such a value.

For example, a layer of irregular material can be made of CVD diamonds,of Si₃N₄, of AIN or even of a poly-crystal material such as, notably,poly-crystal silicon, and the like. Such rough materials can, forexample, be implemented in a SOI (Silicon on Insulator) type structureto improve the heat conductive properties of such a wafer. It iscontemplated that the insulator layer of such a wafer would not be madeof SiO₂ (whose heat conducting properties are poor), but may be made ofone or several materials that have high heat conductivity, such asdiamonds or Si₃N₄. Layers of such materials are generally obtained viaepitaxy. However the surface of such epitaxial layers is rough.

The table below presents examples of the heat conductivity coefficientsfor different materials.

Material Heat conductivity W/m/K Buried oxide of the SIMOX structure 1.6CVD diamond 2 × 10³ AIN >250 Si₃N₄ >150 Si 168

The word “bonding” means putting two surfaces into close contact so thatlinks (for example. Van der Waals forces or hydrogen links) are createdbetween the two surfaces (For example, see “Semiconductor Wafer BondingScience and Technology”, Wiley, 1999, Q.-Y Tong and U. Gösele). Suchprocesses are known. In particular, the published InternationalApplication No. WO 01/97282 describes a process in which a zone ofweakness is created by implanting atomic species. This type of processallows the fabrication of multilayer wafers including a layer ofirregular material. Such implementation allows detachment along theweakened zone such that the remainder of the donor substrate which ispresent after detachment can be recycled. In addition, this type ofprocess results in a wafer whose surface is homogenous (notably in termsof thickness), after detachment along the weakened zone. This type ofprocess thus has a certain number of advantages. Moreover, this type ofprocess results in a wafer whose layer of irregular material (forexample in diamond) has one irregular face turned towards the usefullayer of the wafer.

It is to be understood that the useful layer of the wafer is asuperficial layer (a layer located in the immediate neighborhood of thewafer surface), in which components will be created. In addition, itwould be of interest to obtain multilayer wafers in which a layer ofirregular material has a regular face that is turned towards the usefullayer of the wafer. Returning to the example of SOI type wafers havingan insulator layer that is made of one or several irregular materials,this would allow the manufacture of an interface between the usefullayer and the insulator layer that is as regular as possible. Such astructure would in particular improve the electric characteristics ofthe wafer.

SUMMARY OF THE INVENTION

Presented is a method for manufacturing a multilayer semiconductorstructure that includes an irregular layer. The method includesproviding a layer of irregular material on a donor substrate. Theirregular layer has a flat face at an interface with the donorsubstrate, and has an opposite, irregular face. A weakened zone iscreated at a predetermined depth within the donor substrate. Anintermediate layer of material is provided that covers the irregularface of the irregular layer, the intermediate layer providing asubstantially flat surface. The substantially flat surface of theintermediate layer is then bonded to a receiver substrate, and the donorsubstrate is detached along the weakened zone to form the multilayersemiconductor structure. The multilayer structure includes an usefullayer, the irregular layer, the intermediate layer and the receiversubstrate, wherein all of the irregular material of the irregular layeris present in the structure.

In an advantageous embodiment, the method includes treating thesubstantially flat surface of the intermediate material layer prior tobonding. The weakened zone may be formed by implanting atomic speciesinto the donor substrate to a controlled mean implantation depth, and aheat treatment may be used to detach the donor substrate from themultilayer semiconductor structure. Advantageously, the irregularmaterial layer may be deposited on the donor substrate, and chemicalvapor deposition (CVD) may be used.

In a preferred embodiment, the intermediate layer is provided prior tocreating the weakened zone in the donor substrate. In a variation, theweakened zone is created in the donor substrate prior to providing theintermediate material layer. In yet another variation, the weakened zoneis created in the donor substrate prior to providing the layer ofirregular material on the donor substrate. Atomic species may beimplanted into the donor substrate to a controlled mean implantationdepth to form the weakened zone, and the donor substrate detached alongthe weakened zone by exposing the wafer to an appropriate heat budget.Alternately, a detachable donor substrate having a weakened zone may befabricated. The weakened zone may be created by at least one ofproviding a porous region in the donor substrate, providing a reversiblebonding interface between two wafers that comprise the donor substrate,or implanting atomic species into the donor substrate with a dosage thatrequires a predetermined amount of mechanical energy to detach the donorsubstrate along the weakened zone.

The useful layer of the multilayer semiconductor structure mayadvantageously be made of at least one of silicon (Si),silicon-germanium (SiGe), germanium (Ge), silicon-carbon (SiC),gallium-nitride (GaN), gallium-arsinide (GaAs), or a Group (III–V)material. In addition, the multilayer semiconductor structure may be asilicon-on-insulator (SOI) type structure. A beneficial implementationincludes providing a layer of electrical insulator material between theuseful layer and the layer of irregular material. In this case, theelectrical insulator material may be made of silicon-oxide (SiO₂) orSi₃N₄, and may be about 50 Å thick.

The present method advantageously results in a multilayer semiconductorstructure that includes a layer of irregular material having a regularface that is positioned towards the useful layer. For SOI type wafershaving an insulator layer that is made of one or several irregularmaterials, the method permits the manufacture of an interface betweenthe useful layer and the insulator layer that is as regular as possible.Such a structure improves the electric characteristics of the wafer. Themethod also avoids any significant loss of matter during theimplementation of the process. Further, the invention permits recyclingof the remains of the substrate. The methods according to the inventionalso permit the manufacture of multilayer wafers having a homogenoususeful layer.

BRIEF DESCRIPTION OF THE DRAWINGS

Other aspects, purposes and advantages of the invention will becomeclear after reading the following detailed description with reference tothe attached drawings, in which:

FIG. 1 is a block diagram depicting an overall representation of theprocess according to the invention, showing in particular threeprincipal embodiments labeled as methods I, II and III, which illustratethat the process can include different alternatives within the stages Ato F;

FIG. 2 illustrates stage A of Methods I and II of FIG. 1;

FIG. 3 shows stage B of Method I of FIG. 1;

FIG. 4 shows stage C of Method I of FIG. 1;

FIG. 5 illustrates stages C and B of Method I of FIG. 1, wherein thesestages take place in the order shown;

FIG. 6 shows stages D to F of Methods I and II of FIG. 1;

FIG. 7 shows stages B, A and C of Method III of FIG. 1, wherein thesestages take place in the order shown;

FIG. 8 shows stage E of Method III of FIG. 1; and

FIG. 9 shows stage F of Method III of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a block diagram representing the principal stages that can beimplemented in a process according to the invention. The invention canbe implemented to create a multilayer wafer comprising a useful layerwhich can in particular (but not restrictively) be made of at least oneof the following materials: Si, SiGe, Ge, SiC, GaN, GaAs, III–V. Inaddition, the structure may be, in particular, of a silicon-on-insulator(SOI) type.

As explained below, it is possible to optimize the electriccharacteristics of the interface with the useful layer by using a thinlayer of electrical insulator material between the useful layer and thelayer of irregular material. This material can for example be in SiO₂ orin Si₃N₄. Such a layer of electrical insulator material can have athickness of about 50 Å.

The block diagram of FIG. 1 highlights three principal embodiments thatcan globally comprise the same stages that occur in different orders. Ingeneral, FIG. 1 shows stages A to F. Stage A represents creating a layerof irregular material on a donor substrate. Stage B represents creatinga weakened zone in a donor substrate. Stage C represents flattening anirregular surface of the layer of irregular material, Stage D representspositioning the donor substrate and bonding it onto a receiversubstrate. Stage E represents detaching the donor substrate along theweakened zone. Lastly, stage F represents a thinning and/or finishingstep of the free surface or useful layer that results from thedetachment step of stage E. It should be understood that stage E isoptional, and the present method can be implemented without using stageF.

Below are descriptions of three preferred embodiments of the invention.

Method I

In this first principal embodiment, the stages are performed inalphabetical order: A, B, C, D, E and optionally, F. Thus, a layer ofirregular material 12 is first provided on a donor substrate 10. Thesubstrate 10 is made of a semiconductor material such as silicon. It canin particular be a single-crystal silicon. The substrate 10 correspondsto a donor substrate, part of which will be transferred to anothersubstrate called the receiver substrate. The irregular layer 12 can bemade of a poly-crystal material such as poly-crystal silicon, or even ofa diamond material, silicon nitride or silicon carbide. This isapplicable to all of the embodiments of the invention. Such a materialis typically very hard (in the case of diamonds, for example) which isdifficult to uniformly polish because it is heterogeneous (for example,poly-crystal silicon). Such materials are difficult to polish, andconsequently difficult in general to flatten. Such materials may also behigh cost materials, and thus it is desirable to limit the loss of suchmaterials, due to processing for example, as much as possible.

The irregular layer 12 may be obtained via depositing a material on theflat surface of the donor substrate 10. For example, a CVD (ChemicalVapor Deposition) type technique could be used to deposit a materialonto the donor substrate. It is to be noted that the layer 12 is thusadmittedly an irregular layer, but it includes a flat face 121 at theinterface with the donor substrate 10. In addition, the face of thedonor substrate upon which the irregular material is deposited is alsoflat.

The other face 120 of the irregular layer 12—which is opposite to thedonor substrate 10—has irregularities. Consequently, this face 120cannot be bonded with another substrate while in this state.

Stage A thus corresponds to providing a layer of irregular material 12on the donor substrate 10. It should be understood that in thisembodiment, and in the other embodiments, it is possible at thebeginning of stage A to associate a thin electrical insulator layer withthe surface of the donor substrate 10, prior to depositing the irregularlayer 12. In this case, the electrical insulator layer is insertedbetween the substrate 10 and the layer of irregular material 12. Theinsulator layer can be deposited onto the surface of the donor substrate10 or may otherwise be provided via any known technique. This insulatorlayer can, as already mentioned, be made of, for example, SiO₂ or Si₃N₄;and it can have a thickness of about 50 Å. The role of such an insulatorlayer is to optimize the electrical characteristics of the interfacebetween the layer of irregular material 12 and that which willcorrespond to the useful layer of the finished semiconductor structure.

FIG. 3 shows how a weakened zone 13 is created in the donor substrate 10according to an embodiment. In this preferred embodiment, the weakenedzone 13 is created by implanting atomic species through the layer ofirregular material 12. For example, hydrogen and/or helium ions may beimplanted to form the weakened zone 13, as shown by the arrows in FIG.3. This step corresponds to stage B.

FIG. 4 represents the outcome of the next stage C, wherein the irregularsurface of the irregular layer is flattened. In the preferredembodiment, and in the other embodiments, preferably an intermediatematerial is deposited onto the irregular surface of the layer ofirregular material 12 so as to entirely cover the irregular surface witha given thickness of intermediate material. A surface treatment may thenbe conducted on a surface of the intermediate material. For example, thesurface treatment can be a polishing step. It is also envisaged that(once again for all the embodiments according to the invention), instage C the intermediate material is deposited to cover the layer ofirregular material 12. Moreover, such a deposit directly results in asurface of the intermediate layer whose state (flatness and roughness)is suitable for bonding without any additional surface treatment.

The intermediate material can be an amorphous material. It can forexample be in amorphous silicon, but also in any other amorphousmaterial (for example a silicide, such as titanium silicide (TiSi₂), orpalladium silicide (Pd₂Si)).

A layer of intermediate material 14 is thus provided whose surface statepermits bonding with another substrate. The layer 14 can be depositedvia a chemical vapor deposition (CVD) type technique.

Referring to FIG. 4, an intermediate structure 100 has been made thatincludes the donor substrate 10 having a weakened zone 13, the layer ofirregular material 12 having a face turned towards the donor substratethat is regular or flat, the layer of intermediate material 14 whichentirely covers the irregular layer 12, and whose flat surface 140permits bonding.

FIG. 6 corresponds to stages D, E and F of this embodiment of theinvention. In particular, stage D corresponds to positioning theintermediate structure 100 and bonding it to a receiver substrate 20. Inthis regard, it is the flat surface 140 of the layer 14 which contactsthe likewise flat surface of the receiver substrate 20. Prior to thisbonding, the surface 140 may have received a light surface treatment. Itis to be noted, however, that such a treatment is completely differentfrom the substantial treatment which would have been necessary to enablethe layer 12 to be bonded directly to the receiver substrate 20 in theabsence of the layer of intermediate material. The receiver substrate 20is typically made in silicon, for example in single-crystal silicon.

The next stage E consists of detaching the donor substrate 10 along theweakened zone 13. For this purpose, the weakened zone 13 undergoes, asknown, a heat and/or mechanical action. The weakened zone may have beencreated via implantation, and thus the detachment stage can be carriedout by following a SMART-CUT® type process. A general description ofthis type of process can be found in the publication entitled“Silicon-On-Insulator Technology: Materials to VLSI, 2^(nd) Edition” byJean-Pierre Colinge, Kluwer Academic Publishers, pages 50 and 51.

The bonding interface can be stabilized by applying a heat treatment.Such a stabilizing step can be applied after detachment (stage E), andprior to a possible stage F, in all the embodiments according to theinvention.

Stage F corresponds to a surface treatment of the part of the donorsubstrate 10 which is attached to the irregular layer 12, which is theuseful layer 11. Such surface treatments can include additional thinningof the useful layer, and/or a flattening (for example, by using achemical-mechanic polishing (CMP) technique). The finished structurethus achieved is represented in FIG. 6. This structure is a multilayerwafer comprising a layer of irregular material.

It is to be noted that the face of the layer of irregular material whichis turned towards the useful layer 11 is perfectly flat, which isadvantageous. It is also to be noted that this multilayer wafer was madewithout any loss of matter which is normally associated with processesthat thin the substrates via etching or via other techniques that erodematerials. In addition, it is to be noted that this multilayer wafer wasmade without any flattening difficulties, which may occur when methodssuch as polishing are used to flatten the irregular surface of the layer12. Finally, thanks to the fact that the multilayer wafer was madewithout having to polish the layer 12, not only was a long andfastidious operation avoided, but loss of matter of the layer 12 wasavoided (such losses can be detrimental, for example, when the layer 12is made of an expensive material such as diamonds).

Method II

In this method the stages are performed in the following order: A, C, B,D, E and F. Stage A is equivalent to that described above with referenceto Method I. Thus, in this regard reference can once again be made toFIG. 2.

The next stage C corresponds to flattening the irregular surface 120 ofthe layer 12, which was deposited onto the donor substrate 10. Theflattening step can be conducted under the same conditions as previouslydescribed with respect to Method I. Reference can thus be made to FIG. 4(the only difference being that in this case the weakened zone 13 hasnot as yet been formed).

Stage B is then undertaken to create the weakened zone 13 within thedonor substrate 10. Once again this stage may be carried out byimplanting atomic species. The implanting in this case is through thelayer of intermediate material 14 of the layer of irregular material 12and within a desired thickness of the donor substrate 10. In fact, inall the embodiments of the invention, the implantation characteristicsare defined so that the average thickness of the weakened zone 13 withinthe thickness of the donor substrate 10 is controlled.

It is noted that in reference to FIG. 5, which represents the outcome ofstages C and B for Method II, the weakened zone 13 has a more regularprofile than that of the weakened zone in the case of Method I. This isdue to the fact that the irregular surface of the layer 12 was coveredwith a layer 14 which has a flat surface. Under these conditions, theirregularities of the weakened zone 13 are largely relieved, and theweakened zone assumes a profile similar to a plane despite theirregularities of the layer 12. Thus, method II is a particularlyadvantageous embodiment of the invention.

The next stages D, E and F are equivalent to that described above withregard to Method I and thus reference can once again be made to FIG. 6.It is simply to be noted that in this embodiment (Method II), theoptional flattening and finishing operations of the surface of theuseful layer 11 are diminished in comparison to what might be requiredfor Method I. This results from the fact that the weakened zone 13 is,in the case of Method II, more regular.

Method III

In this principal embodiment, the stages are performed in the followingorder: B, A, C, D, E and F. Stage B corresponds to the creating aweakened zone in the thickness of the donor substrate 10. This weakenedzone can, as in the other embodiments according to the invention, becreated by implanting atomic species into the thickness of the donorsubstrate. It is possible in this embodiment of the invention to carryout the implantation step as described above for Methods I and II sothat detachment can then be conducted by simple heat annealing. It isalso possible to “under dose” the implanting of atomic species, as willbe explained. In every case, a flat weakened zone 13 is obtained asimplantation is not carried out through a layer of irregular material

It is also possible to create a weakened zone via other methods, inparticular by providing a donor substrate 10 that includes a“detachable” area along the zone 13. Such a detachable substrate, inwhich detachment can be conducted by a mechanical action along theweakened zone 13, can be created for example by creation of a porousregion in the thickness of the substrate 10. For this purpose, it ispossible to utilize a thin layer of porous silicon on a single-crystalsilicon substrate, and then to cover this layer of porous silicon withanother layer of single-crystal silicon (obtained for example viaepitaxy). In this regard reference can be made to U.S. Pat. No.6,100,166 (which describes an ELTRAN® type process).

A detachable donor substrate 10 may also be made by bonding twosubstrates 101 and 102 (see FIG. 7), the bonding conditions beingdefined so as to limit the bonding energy. In this case, the bonding isreversible under the effect of a mechanical action. In animplementation, this bonding, for example, brings two layers of oxide1010 and 1020 into contact.

In another variation, a detachable substrate may be created by formingan implanted weakened zone 13 by using an implantation dosage inferiorto that which would be required to create a zone that could be detachedsolely by being subject to a high heat budget. Such an implantation is“under dosed” in comparison to that required, for example, for theimplantation step of a SMART-CUT® type process. The use of anunder-dosed implantation allows the creation of a weakened zone 13wherein the donor substrate can only be detached by applying amechanical constraint (this mechanical constraint being itself appliedafter the weakened zone 13 is subjected to a heat budget to allowcoalescence of this zone).

In all cases, a weakened zone 13 is created in the thickness of thedonor substrate 10, which corresponds to stage B. Then a layer ofirregular material 12 is deposited on the donor substrate 10. Thiscorresponds to stage A. Once again, the depositing step can be carriedout under the same conditions as previously described. The irregularsurface of the layer 12 is then flattened, preferably by covering itwith an intermediate layer 14 as described above. The result of stagesB, A and C for this third embodiment is shown in FIG. 7.

Referring to FIG. 7, an intermediate structure 100 has again beencreated, which includes a weakened zone 13 and a layer of irregularmaterial 12 on a donor substrate 10. This structure can be positioned orturned over for bonding with a receiver substrate 20. Such positioningand bonding correspond to the next stage D. The donor substrate 10 isdetached along the weakened zone 13 (stage E). In the case where theweakened zone 13 is created solely via an implantation step, and withsufficient dosage, detachment can be achieved by simply subjecting thestructure to an adequate heat budget (as for the detachment carried outin methods I and II). If a detachable substrate has been used, amechanical action will be required in most cases to achieve thedetachment. The resulting structure is represented in FIG. 8.

Finally, it is once again possible to thin the resulting wafer and/or totreat its surface. The resulting structure that is finally obtained isshown in FIG. 9.

1. A method for manufacturing a multilayer semiconductor structure thatincludes an irregular layer, comprising: providing a layer of irregularmaterial on a donor substrate to form an irregular layer having a flatface at an interface with the donor substrate and having a opposite,irregular face; creating a weakened zone at a predetermined depth withinthe donor substrate; providing an intermediate layer of material thatcovers the irregular face of the irregular layer, the intermediate layerproviding a substantially flat surface; bonding the substantially flatsurface of the intermediate layer to a receiver substrate; and detachingthe donor substrate along the weakened zone to form the multilayersemiconductor structure that includes a useful layer, the irregularlayer, the intermediate layer and the receiver substrate, wherein all ofthe irregular material of the irregular layer is present in thestructure.
 2. The method of claim 1 which further comprises treating thesubstantially flat surface of the intermediate material layer prior tobonding.
 3. The method of claim 1 which further comprises implantingatomic species into the donor substrate to a controlled meanimplantation depth to form the weakened zone.
 4. The method of claim 1which further comprises heat treating to detach the donor wafer from themultilayer semiconductor structure.
 5. The method of claim 1 wherein theintermediate layer is provided prior to creating the weakened zone inthe donor substrate.
 6. The method claim 1 wherein the weakened zone iscreated in the donor substrate prior to providing the intermediatematerial layer.
 7. The method claim 1 wherein the weakened zone iscreated in the donor substrate prior to providing the layer of irregularmaterial on the donor substrate.
 8. The method of claim 7 which furthercomprises implanting atomic species into the donor substrate to acontrolled mean implantation depth to form the weakened zone.
 9. Themethod of claim 8 which further comprises detaching the donor substratealong the weakened zone by exposing the wafer to an appropriate beatbudget.
 10. The method of claim 7 which further comprises fabricating adetachable donor substrate having a weakened zone.
 11. The method ofclaim 10 which further comprises creating the weakened zone by at leastone of providing a porous region in the donor substrate, providing areversible bonding interface between two wafers that comprise the donorsubstrate, or implanting atomic species into the donor substrate with adosage that requires a predetermined amount of mechanical energy todetach the donor substrate along the weakened zone.
 12. The method ofclaim 1 wherein the intermediate material layer is made of an amorphousmaterial.
 13. The method of claim 12 wherein the intermediate materialis amorphous silicon.
 14. The method of claim 1 which further comprisesdepositing the irregular material layer on the donor substrate.
 15. Themethod of claim 14 which further comprises depositing the irregularlayer by chemical vapor deposition (CVD).
 16. The method of claim 1wherein the useful layer of the multilayer semiconductor structure ismade of at least one of silicon (Si), silicon-germanium (SiGe),germanium (Ge), silicon-carbon (SiC), gallium-nitride (GaN),gallium-arsinide (GaAs), or a Group (III–V) material.
 17. The method ofclaim 16 wherein the multilayer semiconductor structure is asilicon-on-insulator (SOI) type structure.
 18. The method of claim 16which further comprises providing a layer of electrical insulatormaterial between the useful layer and the layer of irregular material.19. The method of claim 18 wherein the electrical insulator material ismade of silicon-oxide (SiO₂) or Si₃N₄.
 20. The method of claim 19wherein the electrical insulator layer is about 50 Å thick.
 21. Themethod of claim 1 wherein the layer of irregular material is made of atleast one of diamonds, Si₃N₄, AlN, or poly-crystal silicon.